As the standard quality demanded in X-radiography increases, it is imperative that quality control methods and devices be instituted to assure conformance with newly developed standards. For example, it is desirable that the center of the X-ray beam in a diagnostic X-ray machine be perpendicular at its center since anything else results in inconsistent radiographs of the same patient from machine to machine or, if the perpendicular is varying, on the same machine at two different times. This lack of consistency whether it be location, shading or intensity makes the diagnosis of a slowly progressing illness difficult for the doctor and sometimes results in incorrect diagnosis. Heretofore, wire cage devices have been used with X-ray machines to form a target which when radiographed can be used to crudely indicate the angular relationship of the X-ray beam at the indicated center thereof. These wire cage devices are disadvantageous since the wire therein must be small and fragile to produce any useful result. They also produce radiographs of low resolution due to the varying effective thickness of the wires to the X-rays. It is therefore difficult to determine exactly the perpendicular of the X-ray beam. The wire cage devices are relatively expensive to make and being fragile, they must be repaired or replaced at regular intervals.
It should be mentioned that newer X-ray standards also require that anode focal spot measurements be obtained, a project that is extremely difficult if the beam is not perpendicular at the spot indicated to be its center by the visual cross hair shadow target, a feature provided in most X-ray machines.